The determination of the steady-state pharmacokinetic profile of fluphenazine decanoate by gas chromatography/mass spectrometry detection.

This study uses the highly sensitive method of gas chromatography/mass spectrometry to compare the basic steady-state pharmacokinetic parameters of two fluphenazine decanoate formulations. Sixteen stable outpatients participated in a two-way crossover design study of the bioavailability of a new formulation of FPZ Dec, i.e., 10 mg/ml, to the standard 25 mg/ml formulation. When compared to a 1 ml injection of the standard formulation (25 mg/ml) over a two-week, steady-state period, we found bioequivalence as evidenced by similar mean areas under the curve (hrs x ng/ml). We did find that the injection volume of the same dose (2.5 ml of a 10 mg/ml formulation) results in a statistically significantly higher maximum serum level of parent fluphenazine. A tendency toward faster time to peak level was observed with the 10 mg/ml formulation but the difference was not statistically significant. Both of these differences are considered too small to be clinically significant. In a subgroup of 10 patients, pre-injection serum fluphenazine levels correlated significantly (Pearson r = 0.78, p < 0.05) with serum prolactin levels.